The present invention relates to an ultrasonic scanning apparatus of the sector scan type.
The ultrasonic scanning apparatus is generally categorized into a sector scan type scanning apparatus and a linear scan type scanning apparatus. In the ultrasonic scanning apparatus of the sector scan type, an ultrasonic probe containing an ultrasonic transducer array sectionally scans an object, using the ultrasonic beam projected from the probe. The image information contained in the echo-wave from the object is displayed on the CRT screen. Since only the echo-waves corresponding to the focal points are received, the echo signals from the transducer elements are delayed by different periods of time. To obtain such delay periods in the conventional probe, N transducer elements arrayed channel 1 to channel N are connected by N switching elements to a delay line. The N switching elements have each n switching contacts. The contacts of the switching elements are coupled with n terminals of the delay line. These contacts are switched according to a deflection angles 0.degree. to .+-..theta..degree. of the ultrasonic beam, so that the echo-wave as specified by each deflection angle can be received.
The conventional switching circuit requires the same number of contacts for each switching element as that of the terminals of the delay line. The number of the terminals of the switching element depends on a maximum deflection angle. Accordingly, for a large deflection angle, a great number of the terminals are needed. The more terminals the more contacts for the switching elements. The switching element with such an increased number of contacts is inevitably large. The large switching element has a large stray capacitance. Electrically, this brings about the crosstalk problem, and degradation of the frequency characteristic of the ultrasonic imaging apparatus.